The mother in my vampire family, is cheerful, domestic (from being family oriented), and had 100% relationship with her children. But she runs up to two of her daughters playing chess, one a young adult who was a Top-notch Toddler and raised to adulthood so studiously as to be gifted in every way along with the Responsible, Emotional control, compassionate, mediator, and good manners traits. The other a teen who has the cheerful (like her mom) and new Loyalty traits.
Mom comes up and starts insulting the young adult daughter, completely unprovoked which of course causes the teenage daughter to "confront bully" on mom, and now everyone has hard feelings because the game gives some the "aggravating conversation" moodlet, a big chuck off the relationships, and if they didn't have bad sentiment toward each other, they do now. All because of an autonomous insult.
Now I don't expect sims to behave perfectly just because their relationship has been flawless to a point. These interactions have been going on with increasing frequency, so for all I know they are holding grudges for past altercations in spite of having already repaired the relationship damage... which FYI takes a lot longer than the one insult it took to throw it into a tail spin.
Anyway, what I would like, is more information from the interface, detailing specifically why a sim may be holding beef on another, which sim specifically is the offender... I have a big 8 person house, and the "swelling bitterness" moodlet tells me someone did something to a sim so they don't like being around that sim, but I have little way of figuring out how to sort the mess if I can't identify the offending sim because of the ambiguous moodlet description. It would also be nice to be able to tell exactly how long, or how close two sims are to burying a hatchet.